The invention relates to a method of fabricating a semiconductor device, and more particularly to a method of producing a silicon nitride film serving as a insulating film of capacitors.
Stacked capacitors or trench capacitors which serve as memory cells of a dynamic random access memory (DRAM) are well known. The conventional method of fabricating the typical stacked capacitor will hereinafter be described in detail with reference to the accompanying drawings. Referring to FIG. 1, a field oxide film 1 which serves to separate a memory cell from other elements of the semiconductor device has selectively been formed on a silicon substrate 2 by the local oxidation of silicon (LOCOS), as shown in FIG. 1, before a polycrystalline silicon film 3A is deposited on the entire region of the silicon substrate 2 including the field oxide film region by chemical vapor deposition (CVD) not shown in FIG. 1. Then, the polycrystalline silicon film 3A is subjected to patterning by means of photolithography and dry etching so as to form a bottom electrode only on the silicon region of the substrate as shown in FIG. 1(b). As shown in FIG. 1(c), a silicon nitride film 4B and a polycrystalline silicon film 5A are deposited in turn on the entire region of the substrate including the field oxide film region. And then, as shown in FIG. 1(d), the polycrystalline silicon film 5A and the silicon nitride film 4B are simultaneously subjected to patterning by use of photolithography and dry etching to form a top electrode and a dielectric film respectively. Further, required in the fabrication process of the stacked capacitor are processes of controlling a conductivity of the capacitor by ion-implantation and heat treatment. Also required in the processes of photolithography and dry etching are the processes of cleaning, applying a resist, baking, exposing, removing a resist and the like.
In recent years, the selective growth techniques of the polycrystalline silicon have been developed to allow formation of the bottom electrode of the stacked capacitor which is disclosed in the specification of the Japanese patent application No. 2-215544 entitled Method of Fabricating a Semiconductor Device. In this prior art, when a polycrystalline silicon film is grown on a silicon substrate, a source gas of a silane system, for example, silane or dichlorosilane or the like, is subjected to a combination of both (1) either thermal decomposition or reduction in a hydrogen atmosphere and (2) doping with a hydrogen chloride gas at a suitable concentration. The source gas doped with the hydrogen chloride gas allows the polycrystalline silicon film to grow on the silicon substrate and also to etch silicon deposited on the silicon oxide film. Further, a low growth temperature of 750 degrees may be selected to suppress growth of a monocrystal silicon. It is possible for the prior art to provide the selective growth of the polycrystalline silicon to the silicon substrate. Consequently, photolithography and dry etching may be omitted from the processes of formation of the polycrystalline silicon film.
However, it is difficult in the set forth prior art to provide the selective growth of the silicon nitride film 4B only to the region of the polycrystalline silicon film 3A, because the source gas includes only silane system gas, for example, silane or dichlorosilane or the like. Thus, it is difficult to provide not only the selective growth of the silicon nitride film 4B serving as the dielectric film on the polycrystalline silicon film 3A serving as a bottom electrode, but also the selective growth of the polycrystalline silicon film 5A serving as a top electrode on the silicon nitride film. It may therefore be assumed that both the silicon nitride film 4B and the polycrystalline silicon film 5A is certainly subjected to pattering by photolithography and dry etching. The patterning process comprises cleaning, coating a resist, baking, exposing, dry-etching and removing a resist and the like. The prior art has many problems of particle-pollution, metal pollution and damaging of the device with deterioration of the characteristics of the device. In general, the degree of deterioration of device quality may be in proportion to the largeness of the number of processes of fabrication of the device. Further, needless time and higher cost are required for fabrication of the device.
On the other hand, the conventional fabrication method of the trench capacitor also has many of the set forth problems.
A trench may conveniently be formed within a silicon substrate serving as a bottom electrode which has been formed thereon with a silicon oxide film by means of patterning and dry etching and the like. Therefore, it is difficult for the prior art to provide the selective growth of the silicon nitride film only on the inner surface of the trench within the silicon substrate. Further, it is also difficult for the prior art to provide the selective growth of a polycrystalline silicon film serving as a top electrode only on the silicon nitride film. Consequently, as unnecessary processes, the silicon nitride film and the polycrystalline silicon film are certainly subjected to patterning by photolithography and dry etching. The prior also has many problems, for example, particle-pollution, metal-pollution and damaging of the device with deterioration of characteristics of the device. Further, unnecessary time and higher costs are required for fabrication of the device.